This invention relates to an adaptive filter for a device for processing television signals, e.g., a television receiver, a video recoder, or a television-capable multimedia device, which serves to separate the interleaved luminance and chrominance components of a composite color signal.
For this separation, filter combinations are increasingly being used which permit a better adaptation to certain image characteristics than single filters. For the filtering, as is well known, brightness and color transitions as well as mosaic structures in the image content are critical. Because of the filter characteristics, this partly results in very disturbing spurious signals which show up in the image as color fringing, xe2x80x9cworm tracksxe2x80x9d, xe2x80x9cdot crawlxe2x80x9d, or moire patterns. The spurious effects produced by the individual filters, e.g., comb, bandpass, or bandstop filters, and their causes are known. Therefore, attempts are being made to achieve disturbance-free separation by combining different filters. Switching directly from one filter to the other is not conducive to this. Soft switching by controlling the individual filter contributions is much better and produces fewer transition effects. In this manner, intermediate states can be set for the filtering using the combining effect of several or all filters; The individual filter contributions are combined into a single output signal using different weighting factors. The determination of the individual weighting factors is controlled by an analysis or decision device which examines the image content in the respective region for critical image structures, with a field or frame storage registering both area-related and temporal image characteristics. Via these analysis values, the filter combination can be adaptively controlled. An example of such an adaptive filter arrangement, which is also suitable for monolithic integration, is described in detail in PCT Patent Application WO 90/13978.
One disadvantage of the prior-art adaptive filters is that the algorithm for controlling the filter contributions is wired in or programmed by the manufacturer. Intervention from outside by the equipment manufacturer or the user is thus nearly impossible, for the program allows only slight modifications to the complicated algorithm, provided one knows where to intervene.
Another disadvantage is that the predetermined algorithm is optimized essentially only for a single operating and image condition and does not take different image sources, receiving conditions, and processing devices into account. For the rest, the algorithm, as a rule, orients itself by the usual test patterns, which convey an optimum impression, but which generally do not look so good in the presence of real television signals, i.e., under subjective viewing conditions.
It is therefore an object of the invention to make it possible to adapt the response of an adaptive filter in the simplest possible manner to different operating conditions and video signals even after the manufacturing process.